1,574 research outputs found
Spatially Resolved Stellar Populations of Eight GOODS-South AGN at z~1
We present a pilot study of the stellar populations of 8 AGN hosts at z~1 and
compare to (1) lower redshift samples and (2) a sample of nonactive galaxies of
similar redshift. We utilize K' images in the GOODS South field obtained with
the laser guide star adaptive optics (LGSAO) system at Keck Observatory. We
combine this K' data with B, V, i, and z imaging from the ACS on HST to give
multi-color photometry at a matched spatial resolution better than 100 mas in
all bands. The hosts harbor AGN as inferred from their high X-ray luminosities
(L_X > 10^42 ergs/s) or mid-IR colors. We find a correlation between the
presence of younger stellar populations and the strength of the AGN, as
measured with [OIII] line luminosity or X-ray (2-10 keV) luminosity. This
finding is consistent with similar studies at lower redshift. Of the three Type
II galaxies, two are disk galaxies and one is of irregular type, while in the
Type I sample there only one disk-like source and four sources with smooth,
elliptical/spheroidal morphologies. In addition, the mid-IR SEDs of the strong
Type II AGN indicate that they are excited to LIRG (Luminous InfraRed Galaxy)
status via galactic starbursting, while the strong Type I AGN are excited to
LIRG status via hot dust surrounding the central AGN. This supports the notion
that the obscured nature of Type II AGN at z~1 is connected with global
starbursting and that they may be extincted by kpc-scale dusty features that
are byproducts of this starbursting.Comment: 56 pages, 39 figures, accepted to A
Spectral Templates from Multicolor Redshift Surveys
Understanding how the physical properties of galaxies (e.g. their spectral
type or age) evolve as a function of redshift relies on having an accurate
representation of galaxy spectral energy distributions. While it has been known
for some time that galaxy spectra can be reconstructed from a handful of
orthogonal basis templates, the underlying basis is poorly constrained. The
limiting factor has been the lack of large samples of galaxies (covering a wide
range in spectral type) with high signal-to-noise spectrophotometric
observations. To alleviate this problem we introduce here a new technique for
reconstructing galaxy spectral energy distributions directly from samples of
galaxies with broadband photometric data and spectroscopic redshifts.
Exploiting the statistical approach of the Karhunen-Loeve expansion, our
iterative training procedure increasingly improves the eigenbasis, so that it
provides better agreement with the photometry. We demonstrate the utility of
this approach by applying these improved spectral energy distributions to the
estimation of photometric redshifts for the HDF sample of galaxies. We find
that in a small number of iterations the dispersion in the photometric
redshifts estimator (a comparison between predicted and measured redshifts) can
decrease by up to a factor of 2.Comment: 25 pages, 9 figures, LaTeX AASTeX, accepted for publication in A
Calculation of the Density of States Using Discrete Variable Representation and Toeplitz Matrices
A direct and exact method for calculating the density of states for systems
with localized potentials is presented. The method is based on explicit
inversion of the operator . The operator is written in the discrete
variable representation of the Hamiltonian, and the Toeplitz property of the
asymptotic part of the obtained {\it infinite} matrix is used. Thus, the
problem is reduced to the inversion of a {\it finite} matrix
Massive Ellipticals at High Redshift: NICMOS Imaging of Z~1 Radio Galaxies
We present deep, continuum images of eleven high-redshift (0.811 < z < 1.875)
3CR radio galaxies observed with NICMOS. Our images probe the rest-frame
optical light where stars are expected to dominate the galaxy luminosity. The
rest-frame UV light of eight of these galaxies demonstrates the well-known
``alignment effect''. Most of the radio galaxies have rounder, more symmetric
morphologies at rest-frame optical wavelengths. Here we show the most direct
evidence that in most cases the stellar hosts are normal elliptical galaxies
with de Vaucouleurs law light profiles. For a few galaxies very faint traces of
the UV-bright aligned component are also visible in the infrared images. We
derive both the effective radius and surface-brightness for nine of eleven
sample galaxies by fitting surface-brightness models to them. We find their
sizes are similar to those of local FRII radio source hosts and are in general
larger than other local galaxies. The derived host galaxy luminosities are very
high and lie at the bright end of luminosity functions constructed at similar
redshifts. The galaxies in our sample are also brighter than the rest-frame
size--surface-brightness locus defined by the low-redshift sources. Passive
evolution roughly aligns the z ~ 1 galaxies with the low-redshift samples. The
optical host is sometimes centered on a local minimum in the rest-frame UV
emission, suggesting the presence of substantial dust obscuration. We also see
good evidence of nuclear point sources in three galaxies. Overall, our results
are consistent with the hypothesis that these galaxies have already formed the
bulk of their stars at redshifts greater than z >~ 2, and that the AGN
phenomenon takes place within otherwise normal, perhaps passively evolving,
galaxies. (abridged)Comment: 28 pages, 14 figures, accepted to ApJ. Uses AASTEX and emulateapj
Location and arrangement of campaniform sensilla in Drosophila melanogaster
Sensory systems provide input to motor networks on the state of the body and environment. One such sensory system in insects is the campaniform sensilla (CS), which detect deformations of the exoskeleton arising from resisted movements or external perturbations. When physical strain is applied to the cuticle, CS external structures are compressed, leading to transduction in an internal sensory neuron. In Drosophila melanogaster, the distribution of CS on the exoskeleton has not been comprehensively described. To investigate CS number, location, spatial arrangement, and potential differences between individuals, we compared the front, middle, and hind legs of multiple flies using scanning electron microscopy. Additionally, we imaged the entire body surface to confirm known CS locations. On the legs, the number and relative arrangement of CS varied between individuals, and single CS of corresponding segments showed characteristic differences between legs. This knowledge is fundamental for studying the relevance of cuticular strain information within the complex neuromuscular networks controlling posture and movement. This comprehensive account of all D. melanogaster CS helps set the stage for experimental investigations into their responsivity, sensitivity, and roles in sensory acquisition and motor control in a light-weight model organism
Optically faint X-ray sources in the CDFN: Spitzer constraints
We investigate the properties of the most optically faint sources in the
GOODS-N area (R > 26.5 AB). Such extremely optically faint populations present
an uncharted territory despite the fact that they represent an appreciable
fraction of the X-ray sources in the GOODS-N field. They are believed to
contain either red AGN at moderate redshifts or possibly QSO at very high
redshift. We compile our sample by first finding the 3.6um IRAC counterparts of
the X-ray sources and searching for the optical counterparts of the IRAC
sources. 35 sources do not have counterparts in the R-band Subaru optical
images. Of these, 18 have HST-ACS counterparts while the remaining have no
optical counterparts. The vast majority of our 35 sources are classified as
Extremely Red Objects (EROs) on the basis of their V-K lower limits. Their
photometric redshifts show that these populate moderate redshifts (median
z~2.8), being markedly different from the already spectroscopically identified
population which peaks at z~0.7. The Spitzer-IRAC mid-IR colours of the sources
which have no HST counterparts tend to lie within the mid-IR colour diagram AGN
"wedge", suggesting either QSO, ULIRG (Mrk231), or early-type galaxy templates
at z>3. A large fraction of our sources (17/35), regardless of whether they
have HST counterparts, can be classified as mid-IR bright/optically faint
sources (Dust Obscured Galaxies) a class which is believed to include many
heavily absorbed AGN. The co-added X-ray spectrum of the optically faint
sources is very flat having a spectral index of Gamma~0.87, significantly
flatter than the spectrum of the X-ray background. The optically faint R>26.5
X-ray sources constitute more than 50% of the total X-ray population at
redshifts z>2 bearing important implications for the luminosity function and
its evolution; considering X-ray sources with 2<z<4 we find good agreement with
a modified PLE model.Comment: Accepted for publication in A&
Childhood solid tumours in relation to population mixing around the time of birth
In a retrospective cohort study of 673 787 live births in the Northern Region of England, 1975 - 1994, we investigated whether a higher level of population mixing around birth was a risk factor for solid tumours, by diagnostic group (Hodgkin's disease, brain and spinal tumours, neuroblastoma, other solid tumours), diagnosed during 1975-2001 under age 15 years. Logistic regression was used to relate risk to population mixing, based on (i) all movers and (ii) incomers from outside the region. Both ward and county district level analyses were performed. There was a decreased risk of brain and spinal tumours with increasing population mixing based on incomers from outside the region (OR for trend across three categories = 0.79, 95% CI: 0.66-0.95, P = 0.01 in the ward level analysis). Although this may be because of chance, it is consistent with a role of exposure to infection and immunological response in the aetiology of these tumours. For other tumour groups, there was no consistent evidence of an association between risk and population mixing
The Unusual Infrared Object HDF-N J123656.3+621322
We describe an object in the Hubble Deep Field North with very unusual
near-infrared properties. It is readily visible in Hubble Space Telescope
NICMOS images at 1.6um and from the ground at 2.2um, but is undetected (with
signal-to-noise <~ 2) in very deep WFPC2 and NICMOS data from 0.3 to 1.1um. The
f_nu flux density drops by a factor >~ 8.3 (97.7% confidence) from 1.6 to
1.1um. The object is compact but may be slightly resolved in the NICMOS 1.6um
image. In a low-resolution, near-infrared spectrogram, we find a possible
emission line at 1.643um, but a reobservation at higher spectral resolution
failed to confirm the line, leaving its reality in doubt. We consider various
hypotheses for the nature of this object. Its colors are unlike those of known
galactic stars, except perhaps the most extreme carbon stars or Mira variables
with thick circumstellar dust shells. It does not appear to be possible to
explain its spectral energy distribution as that of a normal galaxy at any
redshift without additional opacity from either dust or intergalactic neutral
hydrogen. The colors can be matched by those of a dusty galaxy at z >~ 2, by a
maximally old elliptical galaxy at z >~ 3 (perhaps with some additional
reddening), or by an object at z >~ 10 whose optical and 1.1um light have been
suppressed by the intergalactic medium. Under the latter hypothesis, if the
luminosity results from stars and not an AGN, the object would resemble a
classical, unobscured protogalaxy, with a star formation rate >~ 100 M_sun/yr.
Such UV-bright objects are evidently rare at 2 < z < 12.5, however, with a
space density several hundred times lower than that of present-day L* galaxies.Comment: Accepted for publication in the Astrophysical Journal. 27 pages,
LaTeX, with 7 figures (8 files); citations & references updated + minor
format change
A blind test of photometric redshift prediction
Results of a blind test of photometric redshift predictions against
spectroscopic galaxy redshifts obtained in the Hubble Deep Field with the Keck
Telescope are presented. The best photometric redshift schemes predict
spectroscopic redshifts with a redshift accuracy of |Delta-z|<0.1 for more than
68 percent of sources and with |Delta-z|<0.3 for 100 percent, when
single-feature spectroscopic redshifts are removed from consideration. This
test shows that photometric redshift schemes work well at least when the
photometric data are of high quality and when the sources are at moderate
redshifts.Comment: 14 pp., accepted for publication in A
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